A position-measuring device of this type includes a linear or curved measuring graduation extending along a measuring direction, a scanning unit for scanning the measuring graduation, as well as a detection device of the scanning unit that includes a plurality of detector elements which are positioned periodically one after the other along an extension direction and which, during the scanning of the measuring graduation, generate output signals able to be supplied to an evaluation unit. In this context, a plurality of adjacent detector elements of the detection device are interconnected to form in each case a detector group such that their output signals are joined and are able to be supplied as a unified signal to the evaluation unit.
The interconnection of adjacent detector elements to form in each case a detector group is intended to make it possible for a scanning unit having a detection device which is provided for scanning a periodic measuring graduation having a first, fine grating structure, to at the same time also be used for scanning a measuring graduation having a different, coarser grating structure. Reference is made to European Published Patent Application No. 1 308 700.
For example, if the measuring graduation having the coarser grating structure has the n-fold grating constant of the measuring graduation having the first, finer grating structure, then, for instance, in each case n-adjacent detector elements of the detection device are interconnected to form one detector group in order to scan the measuring graduation having the coarser grating constant using the same detection device.
In such position-measuring devices, the measuring graduation is typically formed as a mark graduation in the form of a plurality of marks arranged, e.g., periodically, one after the other along the measuring direction. The measuring direction may be formed both by a straight line (linear position-measuring system) and by a curved, e.g., circularly extended line (in the case of a so-called rotary encoder or angular position measuring system). The detector elements are formed, for example, as photo elements which optically scan the measuring graduation and, in so doing, generate electrical output signals able to be supplied to an evaluation unit.
The individual detector elements of the detection device of the scanning unit may be shaped in a conventional manner with respect to their geometric form such that when scanning the measuring graduation having the first, finer grating constant, a harmonics filtering operation is carried out. That is to say, by the selection of suitable contours for the detector elements, certain specifiable harmonics may be eliminated when scanning the measuring graduation having the smaller grating constant. However, if for scanning the coarser measuring graduation having the larger grating constant, in each case a plurality of adjacent detector elements are combined to form one detector group, then the output signal generated when scanning the coarser measuring graduation has a significant harmonics component that may interfere in the further processing and evaluation of the output signal. Reference is made to German Published Patent Application No. 195 05 176.